1. Field of the Invention
The present invention relates in general to energy accumulating systems for accumulating heat energy or cold energy using surplus electric power and using the accumulated energy in later heating operation or cooling operation and, more particularly, to an improved structure in heat accumulators of such energy accumulating systems using latent heat generated in phase changing of a phase change material (PCM) such as water or polyethylene glycol.
2. Description of the Prior Art
As well known to those skilled in the art, the energy accumulating systems for accumulating heat energy or cold energy are equipped with heat accumulators. In a typical energy accumulating system, the heat energy or the cold energy is accumulated in the heat accumulator using cheap night time electric power. The accumulated energy is, thereafter, used in heating or cooling operation in the daytime.
With reference to FIG. 1, there is shown a typical energy accumulating system having a conventional heat accumulator.
In a cold energy accumulating operation of the system, gaseous refrigerant of high pressure and high temperature which was compressed by a compressor 1 is introduced into a condenser 3 wherein the gaseous refrigerant will be cooled in order to become liquid refrigerant. That is, the refrigerant is subjected to heat exchanging in the condenser 3 so as to be changed in its phase from gas to liquid.
The liquid refrigerant, thereafter, passes through an expansion valve 5 so as to be reduced in its pressure and temperature. The liquid refrigerant of low pressure and low temperature is in turn introduced via conduit 7 into a first heat exchanger 9, which functions as an evaporator. The refrigerant is, thereafter, introduced into the compressor 1.
At this time, the refrigerant passing through the refrigerant conduit 7 absorbs the heat from a heat exchanging pipe 11 of the first heat exchanger 9 before it is introduced into the compressor 1.
Therefore, the refrigerant passing through the heat exchanging pipe 11 exchanges the heat with the refrigerant passing through the refrigerant conduit 7 so that the temperature of the refrigerant in pipe 11 falls. The low temperature refrigerant in the heat exchanging pipe 11 exchanges heat with a phase change material in a heat accumulator 13, thus to be increased in its temperature and to become high temperature refrigerant. The high temperature refrigerant is, thereafter, introduced back into the first heat exchanger 9.
The heat exchanging pipe 11 passing through the heat accumulator 13 is zigzagged or coiled in its profile so as to achieve the desired heat exchanging effect. The phase change material is selected from water, polyethylene glycol and the like. The phase change material absorbs the cold from the heat exchanging pipe 11, thus to be changed in phase from liquid to solid and to accumulate cold energy therein.
In a cooling operation of the system, a phase change material is introduced in liquid phase into the heat accumulator 13 through a lower heat accumulator pipe 15. That liquid phase of the phase change material melts a solid phase of the phase change material disposed about the heat exchanging pipe 11 while passing through the accumulator 13.
That is, the liquid phase of the phase change material inside the lower heat accumulator pipe 15 exchanges heat with the solid phase of the phase change material which is frozen about the heat exchanging pipe 11, thus to become a cool refrigerant. Here, the solid phase of the phase change material was changed in phase from liquid to solid by the above-described cold energy accumulation.
The cool refrigerant or the phase change material is pumped by a pump 19 and supplied to a second heat exchanger 21 through a heat accumulator pipe 17 so as to be used in the cooling operation as follows.
As shown in FIG. 1, since both an upper heat accumulator pipe 20 and a cooling coil pipe 23 pass through the second heat exchanger 21 adjacent to each other, the cool refrigerant or the cool phase change material in the upper heat accumulator pipe 20 exchanges heat with a refrigerant in the cooling coil pipe 23, thus reducing the temperature of the refrigerant in the cooling pipe 23.
The low temperature refrigerant in the cooling coil pipe 23 is in turn introduced into a cooling coil 25 wherein the refrigerant absorbs the outside heat. Thereafter, the refrigerant is pumped by a pump 27 so as to be introduced into a cooler 29 wherein the refrigerant is subjected to heat exchanging. This refrigerant after the heat exchanging in the cooler 29 is in turn introduced into the second heat exchanger 21.
Meanwhile, when the refrigerant circulating passage in order of the compressor 1, the condenser 3, the expansion valve 5 and the first heat exchanger 9 is reversed, the above heat accumulating system will carry out a heating operation. At this time, the phase change material in the heat accumulator 13 should be substituted with another phase change material suitable for used in the heating operation.
The above heat energy and cold energy accumulating system is provided with one heat accumulator which is commonly used in both the heating operation and the cooling operation while changing the type of phase change material used in the accumulator when switching between heating and cooling operations.
However, the above energy accumulating system has a shortcoming. That is, the temperature difference between the heat exchanging pipe 11 and the phase change material located about the pipe 11 in the heat accumulator 13 is relatively large so that much of the energy available for exchange is not able to be exchanged. Such a high loss of the potential heat exchanging limits both the heat transferring efficiency and the thermodynamic efficiency during both the heat energy accumulation and the cold energy accumulation. In this regard, the heat accumulator should be enlarged in its size in order to achieve the desired operational efficiency.
Furthermore, it is very difficult to extract a desired amount of energy from the above energy accumulating system.
Another problem of the above energy accumulating system is that the phase change material in the heat accumulator can not be commonly used in both the heating operation and the cooling operation but must be replaced by another phase change material whenever the operation is altered between the heating operation and the cooling operation. This is caused by the fact that the phase change material used in the heat energy accumulation should have a different melting point than the phase change material used in the cold energy accumulation.